In retail or commercial facilities, radio frequency (RF) networks are used to communicate information between remote devices, such as bar code readers and data terminals, and a central computer. In commonly assigned U.S. Pat. No. 5,029,183, for "Packet Data Communication Network", which is hereby incorporated by reference, a data communications network includes a number of remote devices, and a spread spectrum RF link for sending packetized data to a host computer and for receiving an acknowledge signal and data from the host computer.
To permit a remote device to communicate on a selected spread spectrum data communication network, it is required that the remote devices obtain and store information relating to parameters of the spread spectrum radio RF link for that particular network. The parameters which are required to permit communications include the frequency of operation and the pseudo-random chipping sequence of the selected spread spectrum network. Further, a new remote device often obtains and stores various network configuration information, such as, for example, what other equipment is available on the network, the identity of other network members, and its own identity in the network.
In U.S. Pat. No. 5,029,183, an initialization procedure is described, in which, each remote device has an RS-232 connector which is temporarily coupled to the host computer. The pseudo-random chipping sequence and the operating frequency of the particularly spread spectrum network, and various other network information, are communicated, via the temporary RS-232 link, from the host computer to the remote device. The remote device then stores the received information in non-volatile memory. After the initialization procedure, the RS-232 connector is uncoupled from the host computer, and subsequent communications between the remote device and the host computer are made by way of the spread spectrum RF link, utilizing the chipping sequence and the operating frequency stored in the non-volatile memory of the remote device.
After remote devices have been initialized, it is often desired to change the chipping sequence of the network for security or other reasons. For example, the chipping sequences for each network can be made directly and uniquely dependent on the host computer's serial number. If the host computer is replaced, it is required to re-initialize the chipping sequence in each remote device so as to conform to the new unique chipping number of the network. In the U.S. Pat. No. 5,029,183, this re-initialization requires that the RS-232 connection between the remote device and the host computer be used.
In a typical retail or commercial facility utilizing a spread spectrum RF network, it is possible that the remote devices are widely distributed and/or that the remote devices are incorporated in large, non-movable devices. Accordingly, it is often difficult to connect each remote device, via a RS-232 link, to the host the computer to accomplish the above-described initialization and/or re-initialization procedure of the remote device.
To facilitate a periodic RS-232 connection between portable, rechargeable type remote devices and the host computer, it is known to build a RS-232 connection into a charging cradle (herein after referred to as a charging/communicating module). When the remote device is placed in the charging/communication module to be recharged, the RS-232 link is established between the remote device and the host computer, and appropriate initialization and/or re-initialization communications can be effected via the RS-232 link. However, it is known that the portable remote devices may not be placed in the charging/communicating module for long periods of time, and therefore, the re-initialization of the remote device is delayed. Further, during initialization, it is often inconvenient, due to physical layout of the facility, to place each portable device in a charging/communication module, to effect initialization. Still further, the charging/communication module can not be used for remote devices that are incorporated into devices that are not easily portable.
As can be appreciated, as an alternative to connecting the remote device via RS-232 to the host computer, it would be desirable to initialize and/or re-initialize a remote device via the spread spectrum RF link that is used during normal operation. However, to communicate over the spread spectrum link, the remote device must first know the pseudo-random chipping sequence for that particular link. Without knowledge of the pseudo-random chipping sequence, the remote device can not properly interpret received data.
It is theoretically possible for a non-initialized remote device to obtain initialization information, via the spread spectrum RF link, from the host computer, by sequentially cycling through every possible pseudo-random chipping sequence for each possible operating frequency. When the correct combination of pseudo-random chipping sequence and operating frequency is reached, the spread spectrum RF link between the host computer and the remote device channel is established, and the relevant initialization data can be transmitted. However, this approach is impractical due to the large number of possible pseudo-random chipping sequences available in a typical spread spectrum RF data communication network. An inordinate amount of time and energy would be required to accomplish the initialization of each remote device in this manner.